1. Technical Field
The present invention relates to an venting system and more particularly to an venting system for use with a wheel bearing and lubrication system.
2. Background Art
In translational and rotational devices generally and particularly on the wheels of most vehicles such as trucks and trailers, hubcaps are used to maintain oil or grease in the wheel bearings. In addition, hubcaps help exclude external contaminants and prevents them from coming into contact with the wheel bearings within the wheel hub cavity. External contaminants can substantially shorten the life of the wheel bearings.
The interior of the wheel hub cavity is partially filled with oil or grease so that the wheel bearings are lubricated. Friction resulting from the rotating bearings heats the lubricant and the air space within the hubcap causing the enclosed lubricant and air to expand, thereby increasing ambient pressure in the cavity. The characteristic "pumping" action normally associated with the operation of the oil seals used with wheel bearings further tends to raise the ambient pressure. This increased pressure in the wheel hub cavity can become great enough to damage related components such as the oil seal the seal between the hubcap and the wheel hub or even the hubcap itself. Damage to these components can cause leakage of lubricant from the wheel hub cavity and hubcap, resulting in insufficient bearing lubrication.
Moreover, with non-driving axles having hollow spindles, there is a tendency for moisture and condensation to build up in the axle tube during use. That moisture in the axle tube is sometimes forced out of the tube at the spindle end and into the wheel hub cavity when the axle tube is tilted or when pressure builds up in the axle tube. Thus, while the hub cap may prevent entry of some contaminants, it does not prevent the build up of moisture and debris in the axle tube and the wheel end cavity.
Accordingly, it has been necessary to incorporate a venting device at the wheel end assembly to relieve the pressure developed within the wheel hub cavity and to permit moisture to escape. Prior attempts to address these problems have used valve elements positioned in a vent passage formed in the hubcap for permitting air to pass through the vent, in order to reduce internal pressure, while excluding passage of contaminants. However, these valve vent devices also permit lubricant flow out of the hubcap during venting, this results in excessive loss of lubricant over time. In addition, these devices are often unduly complicated because they utilize numerous parts and, therefore, are relatively expensive to manufacture.
Other devices attempt to vent a bearing housing while preventing the flow of lubricant from the bearing housing. Prior attempts includes a hubcap with a vent including a vent passage filled with a cylindrical gas permeable plug of bronze porous material which permits air to pass therethrough but assertedly prevents water and other contaminants from passing therethrough. However, these devices are secured in a vent passage formed in the hubcap via an interference or press fit which requires precision machining to ensure the low tolerances necessary for a secure fit. It is well known, however, that precision machining also results in increased manufacturing costs. Further, the outer surfaces of the prior art vent plugs are directly exposed to the outside work environment and therefore may become undesirably blocked by grit and other contaminants, severely hindering the venting action of the porous material.
As an alternative, a prior art vented hub cap has been provided with a combination of valves at the hub cap, wherein an external check valve relieves pressure and an internal valve remains tightly sealed to prevent lubricant from leaking out and contamination from flowing in.
As seen from the foregoing, there is a need for a vent system for the wheel end assembly which permits air to pass therethrough but which prevents the passage of water and other contaminants, wherein the venting device can be simply and inexpensively manufactured and secured to the wheel end assembly. Moreover, the need exists for a venting system that avoids pressure build-up and that equilibrates the pressure between the axle tube and atmosphere.